Two-gap s± -wave superconductivity at an oxide interface

After half a century of debate, superconductivity in doped SrTiO_3 has come to the fore again with the discovery of interfacial superconductivity in the LaAlO_3/SrTiO_3 heterostructures. While these interfaces share the interesting properties of bulk SrTiO_3 , quantum confinement generates a complex band structure involving bands with different orbital symmetries whose occupancy is tunable by electrostating doping. Multigap superconductivity has been predicted to emerge in LaAlO_3/SrTiO_3 at large doping, with a Bose-Einstein condensation character at the Lifshtiz transition. In this article, we report on the measurement of the upper critical magnetic field Hc2 of superconducting (110)-oriented LaAlO3 /SrTiO3 heterostructures and evidence a two-gap superconducting regime at high doping. Our results are quantitatively explained by a theoretical model based on the formation of an unconventional s±-wave superconducting state with a repulsive coupling between the two condensates.